A wireless sensor network (WSN) is one of essential techniques in the ubiquitous era and is greatly highlighted along with the rapid development of wireless communication and network theories. The wireless sensor network may be utilized for industrial vehicles, home automation, militaries, agriculture, health care, and other various fields. The design of the wireless sensor network system has a very close relation with a specific application program field. In the case of an industrial application, the wireless sensor network should have features such as real-time transmission, low energy consumption, high security, scalability and tenacity.
As specifications for physical layers and link layers of such a sensor network, IEEE 802.15.4 (Low-Rate Wireless Personal Area Network) is settled, and various application products of ZigBee using the same have been put into the market in various fields. In addition, IEEE 802.15.4 suggests wireless connection where a physical (PHY) layer and a medium access control (MAC) layer are defined.
After IEEE 802.15.4 is open to the public, many researchers have suggested a lot of improvements, which result in the improvement of performance of the corresponding specifications. For example, a performance analysis for the GTS allocation mechanism has been already introduced, and a traffic scheduling method for improving the energy efficiency of a network has been proposed. In addition, the implied GTS allocation mechanism has also been proposed for improving the utilization of GTS bandwidth, and the message scheduling method has been introduced for scalability and improvement of the real-time performance of industrial applications. In addition, the adaptive GTS allocation method has been proposed for improving the delay and fairness. However, despite such endeavors, IEEE 802.15.4 still has drawbacks in traffic scheduling due to inherent limitations of the specification.